The present invention relates generally to internal combustion engines and, more particularly, to homogenous charge compression ignition engines and barrel engines.
Internal Combustion Engine Configurations
Internal combustion engines have wide applicability in both mobile and stationary power production applications. The most common type of internal combustion engine is a crank driven reciprocating piston engine. This type of engine includes a cylinder with a moveable piston position therein, and defines a combustion chamber between a closed end of the cylinder and the piston. A rod interconnects the piston with an offset journal on a rotatable crankshaft such that rotation of the crankshaft causes the piston to reciprocate upwardly and downwardly within the cylinder. While traditional crank driven engines are the most common, numerous other engine configurations have been proposed and used. One example is the Wankel rotary engine wherein a lobed rotor rotates within a housing to create expanding and contracting combustion chambers.
Another internal combustion engine configuration is shown in FIG. 1. This engine configuration has gone by various names, including barrel engine, axial engine, axial piston or cylinder engine, cam engine, swash ring or plate engine, crank plate engine, cam or wave cam engine, wobble plate engine, and radial or rotary engine, among others. For purposes of the present application, these types of engines will be referred to as barrel engines. However, it should be understood that the term xe2x80x9cbarrel engine,xe2x80x9d as used herein, is not limited to the specific configurations illustrated, but instead refers to similar designs as well.
The engine 10 in FIG. 1 is merely representative of the general configuration of the engine referred to herein as a barrel engine. It includes a crankshaft or power shaft 12 with a plurality of cylinders arranged about the power shaft 12, though single cylinder variations are possible. The central axis of each of the cylinders 14 may be generally parallel to the power shaft 12. Alternatively, the axes of the cylinders 14 may be tilted outwardly or inwardly with respect to the power shaft 12. A cam plate or track 16 is preferably connected to the power shaft 12 such that the two rotate in unison. The track 16 surrounds and extends outwardly from the power shaft 12 and has an undulating cam surface 18. As the power shaft 12 is rotated about its longitudinal axis, the cam surface 18 of the track 16 undulates closer to and farther from the cylinders 14. Pistons 20 are moveably positioned in the cylinders 14 and define a combustion chamber 22 between each piston and the upper end of its respective cylinder 14. The pistons 20 are interconnected with the track 16 such that as the track rotates, the pistons are caused to reciprocate within the cylinders 14. In the illustrated embodiment, connecting rods 24 have upper ends interconnected with the pistons 20 and lower ends with rollers 26 that ride on the cam surface of the track 16. Alternatively, pistons in such an engine may be more directly interconnected with the track, such as rollers or slides directly connected to the pistons.
As will be clear to those of skill in this art, as the power shaft 12 rotates and the pistons 20 reciprocate within their respective cylinders, the various strokes of a combustion cycle can be defined. Typically, the cam surface 18 of the track 16 has a generally sinusoidal shape, thereby corresponding to the reciprocal motion typical of a crank driven piston. Also, the track is generally disposed in a plane perpendicular to the power shaft and the cam surface is generally disposed at a constant distance from the axis of the power shaft.
Barrel engines maybe either single ended or double ended. In a single ended design, cylinders and pistons are provided in the end of the engine on one side of the track, such as above the track as illustrated in FIG. 1. In double ended designs, cylinders and pistons are provided on both ends of the engine (both above and below the track when positioned as shown in FIG. 1). Another variation includes a track at both ends of the engine and opposed pistons extending towards one another from the two tracks. The tracks typically rotate in unison causing two pistons to reciprocate towards and away from one another within a common cylinder.
Applicant""s prior applications, referred to in the Reference to Related Applications, and incorporated herein by reference, discuss various engine designs generally referred to as Inverse Peristaltic Engines. Applicant considers barrel engines to be a variation within the general class of Inverse Peristaltic Engines, as described in these applications. Other variations on Inverse Peristaltic Engines share certain functional attributes with barrel engines as described within the present application. It should be noted that some aspects of the present invention may be used with engine configurations other than the particular configurations illustrated or described.
Another engine design that has some functional and/or structural similarities to barrel engines, as thus far described, is a type of engine often referred to as a wobble plate engine. FIG. 2A illustrates a schematic of a portion of a wobble plate engine 30. In the barrel engine 10, the track 16 is illustrated as having two low points and two high points corresponding to a complete set of four strokes for a combustion engine. In the wobble plate engine, a plate 32 is interconnected with the longitudinal powershaft 34. The plate 32 is generally planar, but is angled with respect to the powershaft 34 such that it has high and low portions. That is, rather than the 32 being perpendicular to the shaft 34, it is tilted somewhat. Pistons 36 and 38 are in mechanical communication with the plate 32, in a manner similar to in FIG. 1. However, because the plate 32 is generally planar instead of being more complexly shaped, such as the track 16, only two strokes are defined within a single rotation of the plate 32. That is, if the shaft 34 is rotated through one complete revolution, each of the pistons 36 and 38 would experience only a single top-dead center and bottom-dead center. With the barrel engine of FIG. 1, on the other hand, a single rotation of the track 12 causes each of the pistons 20 to travel to top-dead center twice and bottom-dead center twice. Designs similar to the engine 30 have been used for wobble plate compressors. In these compressors, the angle of the plate may be adjusted to adjust the compression ratio of the compressor. Typically, such a compressor has spherical rollers interconnecting the pistons with the plate. An engine may be constructed similarly. The design of FIG. 2A and compressor-like variations are considered to be barrel engines, as defined herein.
Referring now to FIG. 2B, another version of an engine 40 is illustrated. In this engine 40 a shorter longitudinal powershaft 42 connects with an angled cam 44, that is generally triangular in cross-section. The powershaft 42 and angled cam 44 rotate in unison. A wobble plate or piston support plate 46 rides on the upper surface of the angled cam 44, but does not rotate therewith. Therefore, as the angled cam 44 rotates, the piston support plate 46 tilts back and forth. Pistons are interconnected with the piston support plate 46 such that movement of the plate 46 causes reciprocal motion of the pistons. This is again considered a type of barrel engine as defined herein. It differs from the two previous designs in that the piston support plate 46 replaces the rollers for communicating movement between the cam 44 and the pistons.
Other versions of barrel engines, as defined herein, include a type of engine called nutating engine. Examples are shown in U.S. Pat. Nos. 5,992,357 and 6,019,073, both of which are incorporated in their entirety herein by reference. Another barrel engine design, sometimes referred to as a bent-axis engine, is shown in U.S. Pat. No. 1,293,733 to Duby, which is also incorporated herein in its entirety by reference.
Combustion Strategies for Internal Combustion Engines
A variety of combustion strategies have been proposed and/or tested for internal combustion engines. The most common strategy, referred to herein as spark ignition (SI), is illustrated in FIG. 3. Air and fuel are mixed together prior to being drawn into a combustion chamber. The mixture is compressed in the combustion chamber and a spark is then provided to ignite the compressed mixture. This process is used in most gasoline-fueled internal combustion engines. Spark ignited internal combustion engines include both two stroke and four stroke reciprocating piston designs, as well as some less well known varieties. The air and fuel is typically mixed upstream of the cylinder using a carburetor or fuel injectors. The air and fuel mixture for multiple cylinders may be created at a single point, such as with typical carburetors and throttle body fuel injection systems, or fuel and air may be mixed individually for individual cylinders, such as occurs with port fuel injection. A less common approach is to directly inject fuel into the cylinder prior to or during the compression stroke. Whatever the variation, spark ignition engines are characterized by the fact that combustion is initiated by the introduction of a spark to a compressed air and fuel mixture. Spark ignited engines have the benefit that combustion timing, also referred to as combustion phasing, is easily controlled. Because combustion is initiated by the introduction of a spark, combustion timing can be controlled by controlling spark timing. Spark ignition engines also tend to be relative compact and less expensive than some other types of engines. A drawback to spark ignition engines is lower fuel efficiencies than some other types.
Another well known combustion strategy is the approach used with Diesel engines, illustrated in FIG. 4. In a Diesel, air, without fuel, is drawn into a combustion chamber and compressed. Once the air is partly or completely compressed, fuel, typically Diesel fuel, is injected into the compressed air. The introduction of the fuel into the compressed air, under the appropriate conditions, causes the fuel and air mixture to combust. Variations on the diesel strategy include the introduction of fuel at more than one stage in so called stratified-charge Diesel engines. In a stratified-charge Diesel engine, the air fuel mixture is intentionally manipulated to create areas of richer and leaner fuel concentrations. Often this is accomplished by compressing an initially lean mixture and then adding additional fuel to create localized rich areas and to initiate combustion. Stratified-charge or lean combustion approaches have also been used with spark ignition engines. Combustion phasing is also easily controlled in a diesel engine, since fuel injection timing determines combustion timing. Diesel engines offer improved fuel efficiency in comparison to spark ignited engines, and offer the ability to combust less expensive types of fuels. However, Diesel engines tend to be heavier, more expensive and noisier than spark ignited engines. Also, diesels produce high levels of oxides of nitrogen (NOx) and particulate emissions.
Another combustion strategy, referred to herein as homogenous charge compression ignition (HCCI), is illustrated in FIG. 5. In HCCI, a mixture of air and fuel is drawn into a combustion cylinder. The mixture is then compressed until the mixture autoignites, without the introduction of a spark. Variations on HCCI include injection of fuel directly into the cylinder at some point during the compression stroke so as to promote a substantially premixed charge. The HCCI combustion strategy has been referred to by various names, including controlled auto-ignition combustion (Ford), premixed charged compression ignition (Toyota and VW), active radical combustion (Honda), fluid dynamically controlled combustion (French Petroleum Institute), and active thermo combustion (Nippon Engines).
HCCI offers several benefits over spark ignition and Diesel strategies. First, HCCI offers the potential for significantly increased fuel efficiency. Second, emissions from HCCI are more manageable than for other strategies. HCCI combustion is significantly cooler than conventional combustion and therefore has significantly lower NOx emissions. HCCI also produces less particulate emissions than a diesel engine. Additionally, the absence of locally rich regions found in conventional Diesel engines reduces or eliminates particulate emissions and smoke. The benefits and drawbacks to HCCI, as well as strategies for controlling HCCI, are more extensively discussed in SAE paper no. 1999-01-3682, which is incorporated herein in its entirety by reference.
A drawback to HCCI is that combustion phasing is very difficult to control. The autoignition point of a compressed mixture of air and fuel depends on numerous factors, including the exact makeup of the fuel, the temperature of the mixture, the temperature of the cylinder, the makeup and reactivity of any other components present in the combustion chamber, the shape of the combustion chamber, the operating speed of the engine, the operating load of the engine, and numerous other factors. There has thus far been no practical way to effectively control HCCI combustion in an engine subject to normal transients in load and RPM. Unlike diesel and spark-ignited engines, where the phasing of combustion can be controlled by timing when fuel is injected or when a spark is introduced, HCCI engines lack a direct method of controlling the start of combustion.
Another challenge with HCCI is related to combustion rate. Combustion in HCCI engines occurs at multiple ignition points within the combustion chamber and unlike diesel ignition, in which the rate of combustion is controlled by the mixing rate of the fuel jet and oxidizer, pressure rise in HCCI can occur at an extremely rapid and destructive rate unless very lean air-fuel mixtures are used. The requirement for lean air-fuel mixtures limits the maximum power output of HCCI engines to 50-75% of that of equivalent diesel and Otto cycle engines, placing limitations on the markets in which HCCI engines can be used.
Control Strategies for HCCI
Numerous approaches have been proposed for controlling combustion phasing in an HCCI engine. One approach to controlling the combustion phasing of an HCCI engine is to adjust the compression ratio of the engine. The mixture of the air and fuel will autoignite once it is sufficiently compressed. However, the amount of compression necessary to initiate combustion depends on numerous factors. By varying compression ratio, combustion phasing can be controlled. Higher compression ratios result in earlier combustion and lower compression ratios result in later combustion, or a lack of combustion. Several variable compression ratio engine designs have been proposed, and in some cases, built. These engines suffer from mechanical complexity and increased costs. Additionally, depending on the method used to vary the compression ratio in the engine, changes cannot be made quickly enough to adequately control combustion phasing in an HCCI engine. Also, some designs restrict the placement of valves and create crevice areas in the combustion chamber, thereby leading to lowered efficiency and increased emissions. Such a design is disclosed in SAE paper 1999-01-3679, which is incorporated herein by reference.
Another method for controlling combustion phasing in HCCI engines is to control the temperature of the intake air. As the intake air temperature is increased, with all other conditions held constant, combustion will occur earlier. Reducing the temperature of the intake air delays combustion. Therefore, by controlling the intake air temperature, combustion phasing may be controlled to some extent. Drawbacks to this approach include reductions in volumetric efficiency as intake air temperature is increased and complications related to the provision of heated intake air. Precise control of the intake air temperature at the combustion chamber is also difficult, and the range of adjustment available with this approach is quite limited.
Fuel blending is an additional method for controlling HCCI combustion phasing. Different types of fuels autoignite under different conditions. Therefore, by blending two or more fuels with different propensities to autoignite, combustion phasing can be adjusted. This approach is typically limited to stationary applications. Obvious drawbacks include complications associated with redundant fuel systems and the need for an infrastructure to support distribution of disparate and exotic fuels.
SAE Paper 2000-01-0251 (incorporated herein by reference) discusses the use of residual exhaust gas as a method of controlling HCCI combustion phasing. As the amount of exhaust gas introduced to the combustion chamber is increased, combustion occurs earlier. Drawbacks to this approach included a limited range of control, reduced power and efficiency at high residual levels, and the requirement for high residual levels under certain conditions.
U.S. Pat. Nos. 5,832,880 and 5,875,743 to Dickey propose the use of water injection to control combustion phasing. Water is introduced either in the intake manifold or directly into the combustion chamber. The introduction of water into the combustible mixture delays the onset of combustion. This approach requires the provision of a very controllable water injection system and there is some concern that the injection of water into the combustible mixture may increase engine wear. Also, this approach has not provided adequate control according to researchers in the field.
Yet another approach to HCCI combustion phasing control is proposed in U.S. Pat. No. 6,260,520 to Van Reatherford (incorporated herein by reference). This patent proposes providing a secondary compression device designed to provide additional compression of the mixture in the combustion chamber. In this patent, a secondary boost piston is provided in the cylinder head such that movement of the piston increases and decreases the combustion chamber volume. In operation, the mixture of air and fuel is first compressed by the primary piston. Then, the secondary piston is moved to further increase the compression in the combustion chamber until the mixture autoignites. The timing of the movement of the secondary piston controls the onset of combustion, thereby allowing control of combustion phasing. This design is mechanically complex and increases the crevice volume in the combustion chamber.
Variable valve timing has also been proposed as a method of controlling combustion phasing. By controlling the valve timing of an engine, the effective compression ratio can be somewhat modified.
Despite substantial effort by numerous parties, no control strategy has proven particularly effective at regulating HCCI combustion phasing. This is particularly true where the HCCI engine would experience fast changes in speed and load.
The present invention improves on the prior art with numerous aspects applicable to barrel engines and/or homogenous charge compression ignition engines, as well as aspects with wider applicability. In one embodiment of the present invention, a homogenous charge compression ignition barrel engine includes an engine housing with a first and second end. An elongated power shaft is longitudinally disposed in the engine housing and defines a longitudinal axis of the engine. A plurality of cylinders surround the longitudinal axis with each cylinder having a closed end and an open end. Each cylinder has a central axis. The open ends of the cylinders are each generally directed toward the first end of the housing. An intake system is operable to introduce a combustible mixture of air and fuel into each of the cylinders. A track is disposed between the first end of the housing and the open ends of the cylinders such that a portion of the track is disposed generally in alignment with the central axis of each of the cylinders. The track has a cam surface that longitudinally undulates with respect to the open ends of the cylinders. A portion of the cam surface is disposed generally in alignment with the central axis of each of the cylinders. The track and the cylinders are rotatable with respect to each other such that the undulating cam surface moves with respect to the open ends of the cylinders. A piston is moveably disposed in each of the cylinders such that a combustion chamber is defined between the piston and the closed end of the cylinder. Each piston is mechanical communication with the cam surface of the track such that as the cylinders and the track move with respect to each other, the pistons reciprocate within the cylinders. Each cylinder is operable to compress a combustible mixture until the mixture auto ignites, without the introduction of a spark.
The homogenous charge compression ignition barrel engine may also include a variable compression ratio device operable to adjust the longitudinal position of the track with respect to the open ends of the cylinders, such that the compression ratio of the engine is adjusted. In some embodiments, the central axis of the cylinders are parallel to the longitudinal axis of the engine. The track may be disposed generally in a plane that is perpendicular to the longitudinal axis of the engine with the cam surface disposed at a generally constant distance from the longitudinal axis of the engine.
In one version of the engine, the track is in mechanical communication with the power shaft such that they rotate in unison. In an alternative version, the track is in mechanical communication with the engine housing such that the track and the engine housing do not rotate with respect to each other. In this embodiment, the cylinders and the power shaft are in mechanical communication such that the cylinders and power shaft rotate in unison with respect to the engine housing.
In some embodiments of the present invention, the undulating cam surface defines a generally sinusoidal shape. In other embodiments, the undulating cam surface defines a non-sinusoidal shape. In non-sinusoidal shape versions of the cam surface, the cam surface may define at least one top dead center position, with the top dead center position being linearly shorter than if the cam surface defined a sinusoidal shape. Alternatively, the non-sinusoidal cam surface defines at least one compression stroke and one expansion stroke, with the compression stroke being slower and the expansion stroke being faster than if the cam surface defined a sinusoidal shape.
In some embodiments of the present invention, the intake system includes intake and exhaust valves and includes a variable valve timing system that allows the opening and/or closing time and/or lift of the valves to be adjustably controlled.
In a double-ended version of the present invention, a second set of cylinders is provided between the track and the first end of the engine. Moveable pistons are disposed in the second set of cylinders and are also in mechanical communication with the track such that they reciprocate within the second set of cylinders. The second set of cylinders may be used as combustion cylinders or as part of a supercharger for compressing air for the intake system for the other cylinders.
The present invention also provides for a method of converting fuel and air into rotational energy. According to the method, a homogenous charge compression ignition barrel engine, as described above, is provided and the track is rotated so as to position one of the pistons in its upper position. The track is then rotated to move the piston between an upper position and a lower position and a combustible mixture of air and fuel is introduced into the chamber. The track is then rotated to move the piston upwardly and to compress the mixture. Compression continues until the mixture autoignites without the introduction of a spark, such that the mixture combusts. The combustion causes the piston to move downwardly, thereby causing the track to rotate.
As mentioned previously, the homogenous charge compression ignition barrel engine according to the present invention may include a variable compression ratio device. In these embodiments, the invention includes a method of adjusting the compression ratio in order to establish and/or maintain autoignition. A method is also provided for adjusting the compression ratio so as to generally avoid preignition.
According to further aspects of the present invention, a corona discharge device may be used to introduce radicals and ions into the combustion chamber of an engine so as to alter the mixture reactivity of the combustible mixture in the combustion chamber. This in turn alters the combustion phasing of the engine. The corona discharge device preferably is disposed in the intake system of the engine, but may be alternatively positioned in the combustion chamber. The present invention includes a method of using the corona discharge device to adjust the mixture reactivity. The corona discharge device may be used in a homogenous charge compression ignition barrel engine, as described above. The corona discharge device may also be used as part of a method of controlling a homogenous charge compression ignition engine, by adjusting the mixture reactivity so as to adjust combustion phasing.
Further aspects of the present invention include a homogenous charge compression ignition barrel engine, as described above, further including a rapid compression device operable to rapidly increase the compression level in one of the combustion chambers after the piston has at least partially compressed the mixture, and to cause the combustible mixture to autoignite without the introduction of a spark.
The present invention is also directed to various novel rapid compression devices. In one embodiment, the rapid compression device is designed to introduce a charge of hot gas into a combustion chamber and internal combustion engine. The rapid compression device includes a body with a chamber defined therein with an opening communicating with a chamber. An ignition device is operable to ignite the combustible mixture in the secondary chamber, and a gas permeable spark arrestor is disposed in the opening of the chamber such that an ignited combustible mixture in the chamber is extinguished as the mixture is forced through the arrestor. In some embodiments, an igniter is not required in the chamber, with the combustible mixture in the chamber instead being ignited through autoignition by compression. A rapid compression device as just described may be used with a homogenous charge compression ignition engine, or may have other applications. The present invention includes a method of using the above described rapid compression device to provide rapid compression in an internal combustion engine.
An alternative embodiment of a rapid compression method includes the steps of providing an internal combustion engine with a combustion chamber and introducing a mixture of air and fuel into the combustion chamber. The mixture is then compressed and combusted to create a pressurized gaseous combustion product. A portion of the pressurized gaseous combustion product is then captured and substantially all of the remainder of the gaseous combustion produce is exhausted from the combustion chamber. A fresh mixture of air and fuel is then introduced into the combustion chamber and compressed. The held portion of the pressurized gaseous combustion product is then released into the combustion chamber to rapidly raise the compression level.
The present invention further provides for methods of evening out cylinder-to-cylinder combustion phasing variations in an HCCI engine. In one approach, a first corona discharge device is selectively operable to introduce ions and free radicals into the combustible mixture in a first cylinder and a second corona discharge device is selectively operable to introduce ions and free radicals into the combustible mixture for a second cylinder. A controller controls the first and second corona discharge devices to selectively adjust the relative combustion phasing of the first and second cylinders. Alternatively, first and second water injectors may be provided for selectively introducing water to the first and second cylinders, respectively. Once again, a controller controls the first and second water injectors so as to selectively adjust the relative combustion phasing. As another alternative, the temperature of individual cylinders may be separately controlled so as to adjust relative combustion phasing. The same may be done by individually adjusting air-fuel ratios or intake air temperature or exhaust gas recirculation on a cylinder-by-cylinder basis in order to adjust relative combustion phasing.